Retro Atari 7800 Mod: Sega Master System Controller to Atari 2600/7800 Hack : 4 Steps - Instructables
Amazon.com: Hakeeta Game Controller, Joystick Controller with an Operation Button and a Four-way Control, Compatible with Atari 7800, Suitable for All Atari 2600 Systems. : Video Games
Atari 7800 Gamepad compared to a Master System controller : r/atari7800